PowerShell memory leak when use CredSSP

Question

I want to write code to use Powershell and create a new session by CredSSP authentication, but when I monitor the memory usage for this console, I found something is not disposed, so the memory usage grows slowly.

After I use ANTS to check memory leak, then I was found the key point is credssp, but I can't find the way to dispose it or clean this object.

My envionment is: .NET 3.5, PowerShell 2.0, VS 2010, Windows 7 SP1

class Program
{
    static void Main(string[] args)
    {
        for (int i = 0; i < 10000; i++)
        {
            using (PowerShell powershell = PowerShell.Create())
            {
                powershell.AddScript("$account = \"xxx\"");
                powershell.AddScript("$pwd = \"xxx\"");
                powershell.AddScript("$credential = New-Object System.Management.Automation.PsCredential($account, (ConvertTo-SecureString $pwd -AsPlainText -Force))");
                powershell.AddScript("$sessions = New-PSSession -ComputerName localhost -Credential $credential -Authentication Credssp");
                powershell.AddScript("Remove-PSSession -session $sessions");
                ICollection<PSObject> results = powershell.Invoke();
                Console.WriteLine(System.Diagnostics.Process.GetCurrentProcess().WorkingSet64);
            }
        }
        Console.Read();
    }
}